$ 8^{-3}$
Answer: $= \left(\dfrac{1}{8}\right)^{3}$ $= \left(\dfrac{1}{8}\right)\cdot\left(\dfrac{1}{8}\right)\cdot \left(\dfrac{1}{8}\right)$ $= \dfrac{1}{64}\cdot\left(\dfrac{1}{8}\right)$ $= \dfrac{1}{512}$